On the Microsoft Ignite conference we’d already gained some information on this, but now it has been officially announced: Skype for Business Broadcast meetings!
Imagine situations where you want to broadcast a meeting to a larger audience than the (usually) default maximum 250 participants in a meeting on Skype for Business. Soon, you’ll be able to leverage Skype for Business Broadcast meetings for this!

Broadcast meetings will be a service from Microsoft Online / Office 365. It will also make use of other technologies as Bing Pulse and Yammer. No word on costs just yet, but you will be able to use this together with your on-premises Lync or Skype for Business environment
This service will be made available later this year, but you’ll be able to join a preview as of now.

Another big announcement is the availability (also in preview) of PSTN connectivity in Office 365: Voice from the Microsoft Cloud! Also in preview and shipping later this year, Microsoft will offer phone number dialing (and thus also providing phone numbers for inbound dialing) from Office 365.
Together with Azure Express Route (to guarantee bandwidth to the Azure/Office365 datacenters) and the ability to leverage on premises phone lines as well, this closes the gap between on premises and cloud even more.

Now only available for US customers, but expected to be expanded outside of the US later this year.